The invention relates to electrical transmission cables of the type which are woven and typically include a plurality of conductor elements extending in a warp direction of the cable which transmit high frequency signals. Woven cables of this type are being utilized more and more in computer systems, communications systems, and other sophisticated electronic systems. The controlling of the characteristic impedance of the cable so that the impedance of the cable and the input are matched so that a representative and error free output signal is produced is a problem to which much attention must be given. The need for controlling the impedance becomes more acutely necessary when considering the fast operating speeds of present sophisticated electronic equipment wherein the rise time of the switching pulses is faster than one nanosecond. If the characteristic impedance of the cable is not controlled accurately so that the impedance of the line driver and the cable are matched, ringing in the output signal can occur which results in false triggering or other erroneous signals being produced at the output.
Prior attempts to provide controlled impedance cables in flat flexible type cables of the non-woven type are illustrated in U.S. Pat. Nos. 3,634,782 and 3,818,117.
U.S. Pat. No. 4,143,236 illustrates a woven controlled impedance cable wherein each signal line is provided with a ground conductor on each side thereof to control the impedance. The signal conductors are woven in an undulating woven pattern in the cable. The relative distances between the ground and signal conductors are fixed by the woven warp and weft yarns in the cable. The characteristic impedance of the cable is thus accurately controlled.
The spacing between the, ground wires on either side of the signal wire and the signal wire itself determines to a large extent the characteristic impedance of the cable. The closer the ground wires are brought towards the signal wire, the lower the impedance of the cable. The relative distances between the ground and signal conductors are fixed by the woven warp and weft yarns in the cable. The characteristic impedance of the cable is thus accurately controlled. However, a problem exists in such a woven construction, which also includes warp binder yarns between the signal and ground conductors, in that there is a limit to the closeness in the positioning of the ground wires next to the signal wires due to this woven construction. Thus, the characteristic impedance of the cable reaches a point below which lower impedances are difficult to provide in the woven cable.
Accordingly, an important object of the present invention is to provide a woven electrical transmission cable having a low characteristic impedance value and method therefore.
Another important object of the present invention is to provide a woven transmission cable having a controlled characteristic impedance which may be lower than heretofore provided in a woven cable construction.
Still another important object of the present invention is to provide a woven transmission cable having a low characteristic impedance value in which cross-talk between the signal wires is reduced.